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Table 5 Vaccine effectiveness (VE) of TIV against influenza-related hospitalization by early/late season in patients ≥16 years, ≥16–64 years, and ≥65 years

From: Influenza vaccine effectiveness against influenza-related hospitalization during a season with mixed outbreaks of four influenza viruses: a test-negative case-control study in adults in Canada

  Influenza Type Cases Controls Unadjusted Adjusted
   N N VE, % 95% CI VE, % 95% CI
Age ≥ 16 years (all ages) Early season
 All strains 265 423 48.6 27.9, 63.3 54.4a 29.7, 70.4
 Influenza B 148 230 41.0 8.4, 62.1 44.8b 0.3, 69.5
Late season
 All strains 263 412 33.8 6.6, 53.0 29.7c −5.3, 53.1
 Influenza B 198 304 34.1 2.8, 55.4 33.1d −5.2, 57.5
Age ≥ 16–64 years (younger adults) Early season
 All strains 109 131 59.0 27.6, 76.8 65.7e 28.2, 83.6
 Influenza B 55 68 60.1 12.7, 81.8 67.1f 2.7, 88.9
Late season
 All strains 99 140 −8.5 −95.0, 39.6 −36.1g −171.2, 31.7
 Influenza B 67 93 −27.7 −175.5, 36.7 −52.3h −251.6, 34.0
Age ≥ 65 years (older adults) Early season
 All strains 156 292 41.2 9.8, 61.7 52.5i 8.0, 75.5
 Influenza B 93 162 27.4 −25.9, 58.2 36.3j −45.1, 72.0
Late season
 All strains 164 272 48.6 21.3, 66.4 62.4k 29.9, 79.9
 Influenza B 131 211 50.9 21.2, 69.4 69.3l 37.4, 84.9
  1. N number of patients, CI Confidence Interval, TIV trivalent influenza vaccine
  2. Early season defined as admissions prior to the admission date of the median influenza case enrolled; Late season defined as admissions after the date of admission of the median influenza case enrolled
  3. Covariate (p value in model):
  4. a Influenza vaccination (<0.001), age (0.116), antiviral use before onset of illness (0.821), admission from long term care facility (0.001), obesity (0.017), exposed to children aged <5 years in household (0.536), current or past smoker (0.015), medications before onset of illness (0.325);
  5. b Influenza vaccination (0.049), age (0.099), antiviral use before onset of illness (0.992), admission from long term care facility (<0.001), obesity (0.020), exposed to children aged <5 years in household (0.447), current or past smoker (0.001), medications before onset of illness (0.515);
  6. c Influenza vaccination (0.088), age (0.383), antiviral use before onset of illness (0.988), admission from long term care facility (0.960), obesity (0.859), exposed to children aged <5 years in household (0.030), current or past smoker (0.003), medications before onset of illness (0.007);
  7. d Influenza vaccination (0.082), age (0.150), antiviral use before onset of illness (0.992), admission from long term care facility (0.884), obesity (0.764), exposed to children aged <5 years in household (0.060), current or past smoker (0.002), medications before onset of illness (0.018);
  8. e Influenza vaccination (0.005), age (0.035), antiviral use before onset of illness (0.998), seniors including patient living in the dwelling (0.129), pregnancy (0.994);
  9. f Influenza vaccination (0.045), age (0.021), seniors including patient living in the dwelling (0.061), pregnancy (0.995), (no patients used antivirals before onset of illness);
  10. g Influenza vaccination (0.381), age (0.383), antiviral use before onset of illness (0.992), seniors including patient living in the dwelling (0.046), pregnancy (0.264);
  11. h Influenza vaccination (0.324), age (0.993), seniors including patient living in the dwelling (0.173), pregnancy (0.188), (no patients used antivirals before onset of illness);
  12. i Influenza vaccination (0.027), age (0.151), antiviral use before onset of illness (0.991), frailty index prior to admission (0.057), exposed to children aged <5 years in household (0.179), medications before onset of illness (0.051);
  13. j Influenza vaccination (0.283), age (0.220), antiviral use before onset of illness (0.995), frailty index prior to admission (0.030), exposed to children aged <5 years in household (0.399), medications before onset of illness (0.031);
  14. k Influenza vaccination (0.002), age (0.992), antiviral use before onset of illness (0.993), frailty index prior to admission (0.076), exposed to children aged <5 years in household (0.107), medications before onset of illness (0.397);
  15. l Influenza vaccination (0.001), age (0.673), antiviral use before onset of illness (0.993), frailty index prior to admission (0.043), exposed to children aged <5 years in household (0.467), medications before onset of illness (0.339)